Circuits with high voltage capabilities have wide industrial applications, which include power management systems for use in automobiles. These circuits include power transistors (e.g., high voltage transistor) that operate at a high voltage range (e.g., above 100V) and may also include low voltage transistors that operate at a much lower voltage range (e.g., 1v to 5V). To protect low voltage transistors from high voltage operations, the power transistor may adopt one or more isolation schemes. For instance, one isolation scheme involves forming an isolation structure around a power transistor. The isolation structure may include one or more terminal trenches in a peripheral region that surrounds a transistor region of the power transistor. During high voltage operations, the junctions between the peripheral region and the transistor region may experience a heightened electrical field density, thereby causing a reduction in breakdown voltage. And in certain situations, the reduced breakdown voltage may lead to low level current leakage from the transistor region.